The multi-turn time-of-flight mass spectrometer is a conventional type of mass spectrometer aimed at enhancing the mass resolution by providing a long flight distance within a limited space (for example, refer to Patent Documents 1 and 2 or other documents). In a typical multi-turn time-of-flight mass spectrometer, a plurality of sector-shaped electric fields are used to form a loop orbit having a substantially circular shape, substantially elliptical shape, “figure-8” shape or any other shape. Ions, which are generated from a sample molecule outside (or inside) this loop orbit, are introduced into the loop orbit and made to fly multiple times along the orbit, after which the ions are diverted from the loop orbit, to be introduced to and detected by an ion detector.
In this type of mass spectrometer, increasing the number of turns of ions along the loop orbit increases their flight distance and thereby enlarges the flight-time difference between two ions whose masses (or mass-to-charge ratios, m/z, to be exact) are approximate to each other, making it easier to separate these ions. That is to say, increasing the flight distance enhances the mass resolution.
As described in Patent Documents 1 and 2, this type of mass spectrometer uses a deflector electrode (or “gate electrode”) for introducing ions into the loop orbit, or for diverting the ions flying along the loop orbit from the orbit and directing them toward the ion detector. For example, at an exit gate electrode, which is provided for diverting ions from the loop orbit, the ions can pass through the electrode and continue their flight along the loop orbit when no voltage is applied to the electrode. When a voltage is applied, a deflecting electric field created by the voltage affects the ions, causing them to divert from the original flight path and eventually exit from the loop orbit toward the ion detector. Alternatively, this configuration may be reversed, in which case the voltage applied to the exit gate electrode makes the ions continue their flight along the loop orbit; when the voltage application is discontinued, the ions are allowed to follow the straight path toward the ion detector.
In any case, the traveling direction of the ions is altered by changing the voltage (usually, by turning the voltage on and off) applied to the exit gate electrode. However, this method has the following problem: In the case, for example, the deflecting electric field is set to change the flight direction of the ions and make them fly toward the ion detector, the deflecting electric field cannot exert an adequate force on an ion that is just passing through the exit gate electrode at the timing of application of the voltage to the electrode. This ion deviates from the loop orbit but fails to reach the ion detector. This means that that some ions having specific masses cannot be detected irrespective of the design to obtain a mass spectrum over a broad mass range. Thus, in the previously described conventional mass spectrometers, the mass information relating to ions originating from a sample of interest may possibly be missed due to the presence of the undetectable range relating to the mass.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-116343    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-322429